This application claims benefit of Japanese Application No. 2000-306013 filed in Japan on Oct. 5, 2000, the contents of which are incorporated by this reference.
The present invention relates to image display apparatus having a three-dimensionally decentered optical path. More particularly, the present invention relates to a head- or face-mounted image display apparatus that can be retained on an observer""s head or face.
Image display apparatus designed to observe the image of a single image display device with two eyes have heretofore been known in Japanese Patent Application Unexamined Publication Nos. [hereinafter referred to as xe2x80x9cJP(A)xe2x80x9d] Hei 6-110013, Hei 7-287185, Hei 9-61748, Hei 9-181998, and Hei 9-181999, Published Japanese Translation of PCT International Publication No. Hei 10-504115, etc.
Among them, the image display apparatus of JP(A) Hei 6-110013 splits and folds light rays by using a prism in the shape of an isosceles triangular prism and a mirror. Therefore, correction of various aberrations is performed by using a lens placed in front of the pupil. This makes it difficult to correct aberrations, and at the same time, causes the apparatus to become large in size.
JP(A) Hei 7-287185 uses a plurality of mirrors and performs image formation with a single convex lens. Therefore, it is very difficult to perform assembly adjustment. In addition, appropriate performance cannot be attained. Although the image display device is placed three dimensionally, left and right optical systems are in bilateral symmetry with each other. Therefore, left and right images are in oppositely rotated relation to each other.
In JP(A) Hei 9-61748, display light from an LCD (Liquid Crystal Display) is split by using a half-mirror so as to be observed with two eyes. Because the display light is distributed to the left and right eyeballs, the image for observation is weak in light intensity and hence dark.
JP(A) Hei 9-181998 and Hei 9-181999 have an arrangement using only one reflecting surface and are not sufficiently corrected for decentration aberrations. Therefore, these image display apparatus cannot be applied to recent compact and high-definition image display devices. Further, the field angle is very narrow.
The image display apparatus of Published Japanese Translation of PCT International Publication No. Hei 10-504115 has a very large number of components and requires a very complicated assembling operation. Further, in this case, the image for observation is weak in light intensity and hence dark because a half-mirror is used.
In addition, with the recent achievement of small-sized image display devices, it has also become necessary to reduce the focal length of the viewing optical system. Further, in order to ensure a wide field angle, the focal length needs to be reduced. Consequently, it is difficult to ensure the required back focus, and it is impossible to increase the optical path length within the prism. As a result, it is impossible to increase the number of reflecting surfaces and hence impossible to correct decentration aberrations satisfactorily.
Further, recent image display devices are becoming higher in definition year by year.
The present invention was made in view of the above-described problems with the prior art. An object of the present invention is to provide a wide-field angle and low-cost image display apparatus, e.g. a head-mounted image display apparatus, in which an image from a single image display device is led to two eyes without using a half-mirror, thereby allowing observation of a bright image, and in which at least four reflecting surfaces having curved surfaces are used to form an optical system, thereby facilitating correction of various aberrations to obtain compatibility with recent compact and high-definition image display devices. Another object of the present invention is to further widen the field angle of an image display apparatus such as that proposed previously in Japanese Patent Application No. 2000-48750.
An image display apparatus having a three-dimensionally decentered optical path according to the present invention provided to attain the above-described objects includes an image display device for forming an image for observation on an image display area. The image display apparatus further includes a viewing optical system for leading the image formed by the image display device to a pupil corresponding to a position where an eyeball of an observer is to be placed.
The image display device is a single image display device having a plurality of pixels juxtaposed on a single substrate.
Each pixel located at least in the central portion of the single image display device is arranged to emit an image light beam at such an exit angle that the light beam can be led to the left and right eyes of the observer.
The viewing optical system includes, at least, a left ocular part for leading the light beam to the left eye of the observer; a right ocular part for leading the light beam to the right eye of the observer; and an optical path distributing part for distributing the image light beam emitted from the image display device at the above-described exit angle to the left and right ocular parts.
The left ocular part has at least two reflecting surfaces. At least one of the at least two reflecting surfaces is formed from a rotationally asymmetric curved reflecting surface having the function of correcting decentration aberrations.
The right ocular part has at least two reflecting surfaces. At least one of, the at least two reflecting surfaces is formed from a rotationally asymmetric curved reflecting surface having the function of correcting decentration aberrations.
The left and right ocular parts are arranged so that the plane of a decentered optical path of an axial principal ray formed by the at least two reflecting surfaces of the left ocular part (the plane being a YZ-plane, which is the vertical direction of the observer) and the plane of a decentered optical path of an axial principal ray formed by the at least two reflecting surfaces of the right ocular part (the plane being a YZ-plane, which is the vertical direction of the observer) are approximately parallel to each other (YZ-plane).
The optical path distributing part has optical surfaces arranged in bilaterally rotational symmetry to form left and right optical paths that are not in plane symmetry with each other but in 180-degree rotational symmetry with respect to only a normal line passing through the center of the image display device. The optical path distributing part has at least two pairs of reflecting surfaces for the left and right optical paths as the optical surfaces.
The reasons for adopting the above-described arrangement in the present invention, together with the function thereof, will be described below.
In general, the distance between the human pupils is said to be approximately 64 millimeters on the average and differs among individuals. Therefore, it is preferable that the pupil of the viewing optical system for observation with both eyes should be set long sideways in advance with a view to absorbing the difference in interpupillary distance among individuals in the viewing optical system. In other words, it is preferable that the pupil of the viewing optical system should be an elliptical (or rectangular, etc.) pupil that is long in the horizontal direction of the observer.
In that case, if the longitudinal direction of the pupil and the decentration direction of the ocular part are set in the same direction, it becomes unavoidably necessary to decenter the ocular part to a considerable extent in order to ensure the required effective area. Consequently, the amount of decentration aberrations produced becomes extremely large. To minimize the amount of decentration, the overall size of the optical system has to be increased. In addition, because the human interpupillary distance restricts the extent to which the size of the optical system can be made large sideways, it is impossible to achieve a wide field angle.
For these reasons, setting the decentration direction of the ocular part in the vertical direction of the observer is advantageous for obtaining a wide-field angle, compact and high-performance viewing optical system.
It is, as a matter of course, favorable for the above-described optical path distributing part also to be arranged so that the decentration direction and the longitudinal direction of the pupil are different from each other as much as possible. However, because the light beam from the image display device forms a relay image of small magnification in the optical path distributing part, the required effective area is smaller than in the ocular part. Therefore, the influence due to the above-described reasons is less significant.
In addition, it is desirable that the optical path distributing part should have at least two pairs of rotationally asymmetric curved reflecting surfaces having the function of correcting decentration aberrations.
Further, the optical path distributing part has optical surfaces arranged in bilaterally rotational symmetry to form left and right optical paths that are not in plane symmetry with each other but in 180-degree rotational symmetry with respect to only a normal line passing through the center of the image display device. The optical path distributing part has at least two pairs of reflecting surfaces as the optical surfaces for the left and right optical paths.
In the arrangement of an image display apparatus using a single image display device for observation with left and right eyes (i.e. single-panel binocular vision), optical systems that are in bilaterally plane symmetry with each other are generally employed for the left and right eyes. In this case, the image display device also needs to be placed in a bilaterally plane symmetric position. When a two-dimensionally decentered optical path is used for a viewing optical system, the arrangement is as shown in the image view of FIG. 10. Assuming that the coordinates of the observer are (X0,Y0,Z0) and the coordinates of the image display device are (Xi,Yi,Zi), the image display device is invariably placed in a position where the center of the image display device is lies at the position of bilaterally plane symmetry and the image display device is parallel to the observer""s face. However, when bilaterally symmetric three-dimensional optical paths are used for the arrangement, as shown in the image view of FIG. 11, it is possible to view a single image display device with both eyes even in a case where the image display device is placed in a rotated position about the Xi-axis (i.e. when the image display device is placed so as to face opposite the observer and it is assumed that an Xi-axis is taken in the long-side direction of the image display device, and a Yi-axis is taken in the short-side direction thereof, and further a Zi-axis is taken in the normal direction with respect to the image display device, the image display device can only rotate about the Xi-axis) However, when the optical path is three-dimensionally decentered arbitrarily, rotation of the image about the axial principal ray occurs. In the case of optical systems that are in bilaterally plane symmetry with each other, the images of the image display device that are displayed in the left and right eyes are in oppositely rotated relation to each other. Therefore, the two images seen with the left and right eyes cannot properly be fused into a single image. If it is intended to construct optical paths so that such image rotation does not occur in the bilaterally plane symmetric arrangement, the optical paths become very complicated, causing the apparatus to become large in size.
Further, it is necessary that first left and right reflecting surfaces in the optical path distributing part that reflect the light beam from the image display device should be placed to face opposite to the image display device side-by-side in the longitudinal direction of the image display device. In this case, owing to the fact that the image display device is rectangular and that the pupil of the optical system is elliptical, it is necessary to ensure the above-described reflecting surfaces effective diameter areas that are enlarged in the horizontal direction. For this reason, the optical system must unavoidably be increased in size in order to arrange the optical system so that the left and right optical paths do not interfere with each other within the above-described human interpupillary distance range.
In the arrangement of the present invention, the optical path distributing part forms left and right optical paths that are not in plane symmetry with each other but in 180-degree rotational symmetry with respect to only a normal line passing through the center of the image display device. Therefore, the reflecting surfaces of the left and right optical paths can be readily arranged so that the optical paths do not interfere with each other, without increasing the size of the optical system. Further, regarding the positioning of the image display device, it is possible to rotate the image display device about the normal line passing through the center of the image display device. Accordingly, the degree of freedom for design increases (i.e. when the image display device is placed so as to face opposite the observer and it is assumed that an Xi-axis is taken in the long-side direction of the image display device, and a Yi-axis is taken in the short-side direction thereof, and further a Zi-axis is taken in the normal direction with respect to the image display device, the image display device can rotate about the Xi-axis and also about the Zi-axis). In addition, the rotation of the image occurring when the optical path is three-dimensionally decentered can be absorbed by rotating the image display device because the image rotates in the same direction in the left and right optical paths. At that time, the first left and right reflecting surfaces in the optical path distributing part that reflect the light beam from the image display device have their effective diameter areas rotated together with the rotation of the image display device. Accordingly, it becomes unnecessary to place the above-described left and right reflecting surfaces side-by-side in the horizontal direction as viewed from the observer. Therefore, it becomes easy to ensure the effective diameter area for each reflecting surface and the optical paths within the human interpupillary distance range.
An image view of the arrangement of an optical path distributing prism in Examples 1 and 2 (described later) is shown in FIG. 12, and an image view of the arrangement of an optical path distributing prism in Example 3 is shown in FIG. 13. In Examples 1 and 2, the image rotates through 90xc2x0 in the same direction in the left and right optical paths. Therefore, the image display device is placed in a vertical position (i.e. the horizontal direction of the image display area of the image display device extends in the vertical direction). In Example 3, because three-dimensionally optical paths are formed arbitrarily, the image display device can assume a position in which it is rotated arbitrarily about the Zi-axis (through 15.73xc2x0 in actuality).
Further, in the image display apparatus according to the present invention, a single image display device can be viewed with both eyes. Accordingly, the costs can be reduced extremely.
In addition, each ocular part has at least two reflecting surfaces, and at least one of the reflecting surfaces is formed from a rotationally asymmetric curved reflecting surface having the function of correcting decentration aberrations. Therefore, it is possible to perform favorable aberration correction.
In the present invention, a free-form surface is used as a typical example of a surface having a rotationally asymmetric curved surface configuration. A free-form surface is defined by the following equation. The Z-axis of the defining equation is the axis of a free-form surface.                     Z        =                                            cr              2                        /                          [                              1                +                                                                            {                                              1                        -                                                                              (                                                          1                              +                              k                                                        )                                                    ⁢                                                      c                            2                                                    ⁢                                                      r                            2                                                                                              }                                        ⁢                                          xe2x80x83                                                                                  ]                                +                                    ∑                              j                =                2                            66                        ⁢                          xe2x80x83                        ⁢                                          C                j                            ⁢                              X                m                            ⁢                              Y                n                                                                        (        a        )            
In the equation (a), the first term is a spherical surface term, and the second term is a free-form surface term.
In the spherical surface term:
c: the curvature at the vertex
k: a conic constant
r={square root over ( )}(X2+Y2)
The free-form surface term is given by             ∑              j        =        2            66        ⁢          xe2x80x83        ⁢                  C        j            ⁢              X        m            ⁢              Y        n              =      xe2x80x83    ⁢                    C        2            ⁢      X        +                  C        3            ⁢      Y        +                  C        4            ⁢              X        2              +                  C        5            ⁢      XY        +                  C        6            ⁢              Y        2              +                  C        7            ⁢              X        3            ⁢              C        8            ⁢              X        2            ⁢      Y        +                  C        9            ⁢              XY        2              +                  C        10            ⁢              Y        3              +                  C        11            ⁢              X        4              +                  C        12            ⁢              X        3            ⁢      Y        +                  C        13            ⁢              X        2            ⁢              Y        2              +                  C        14            ⁢              XY        3              +                  C        15            ⁢              Y        4              +                  C        16            ⁢              X        5              +                  C        17            ⁢              X        4            ⁢      Y        +                  C        18            ⁢              X        3            ⁢              Y        2              +                  C        19            ⁢              X        2            ⁢              Y        3              +                  C        20            ⁢              XY        4              +                  C        21            ⁢              Y        5              +                  C        22            ⁢              X        6              +                  C        23            ⁢              X        5            ⁢      Y        +                  C        24            ⁢              X        4            ⁢              Y        2              +                  C        25            ⁢              X        3            ⁢              Y        3              +                  C        25            ⁢              X        3            ⁢              Y        3              +                  C        26            ⁢              X        2            ⁢              Y        4              +                  C        27            ⁢              XY        5              +                  C        28            ⁢              Y        6              +                  C        29            ⁢              X        7              +                  C        30            ⁢              X        6            ⁢      Y        +                  C        31            ⁢              X        5            ⁢              Y        2              +                  C        32            ⁢              X        4            ⁢              Y        3              +                  C        33            ⁢              X        3            ⁢              Y        4              +                  C        34            ⁢              X        2            ⁢              Y        5              +                  C        35            ⁢              XY        6              +                  C        36            ⁢                        Y          7                .                  xe2x80x83                .                  xe2x80x83                .            
where Cj (j is an integer of 2 or higher) are coefficients.
In general, the above-described free-form surface does not have planes of symmetry in both the XZ- and YZ-planes. However, a free-form surface having only one plane of symmetry parallel to the YZ-plane is obtained by making all terms of odd-numbered degrees with respect to X zero. A free-form surface having only one plane of symmetry parallel to the XZ-plane is obtained by making all terms of odd-numbered degrees with respect to Y zero.
In addition, free-form surfaces as the above-described surfaces with a rotationally asymmetric curved surface configuration may be defined by Zernike polynomials. That is, the configuration of a free-form surface may be defined by the following equation (b). The Z-axis of the defining equation (b) is the axis of Zernike polynomial. A rotationally asymmetric surface is defined by polar coordinates of the height of the Z-axis with respect to the XY-plane. In the equation (b), R is the distance from the Z-axis in the XY-plane, and A is the azimuth angle about the Z-axis, which is expressed by the angle of rotation measured from the X-axis.
x=Rxcos(A)
y=Rxsin(A)
Z=D2
xe2x80x83+D3R cos(A)+D4R sin(A)
+D5R2 cos(2A)+D6(R2xe2x88x921)+D7R2 sin(2A)
+D8R3 cos(3A)+D9(3R3xe2x88x922R)cos(A) +D10(3R3xe2x88x922R)sin(A)+D11R3 sin(3A)
+D12R4 cos(4A)+D13(4R4xe2x88x923R2)cos(2A) +D14(6R4xe2x88x926R2+1)+D15(4R4xe2x88x923R2)sin(2A) +D16R4 sin(4A)
+D17R5 cos(5A)+D18(5R5xe2x88x924R3)cos(3A) +D19(10R5xe2x88x9212R3+3R)cos(A) +D20(10R5xe2x88x9212R3+3R)sin(A) +D21(5R5xe2x88x924R3)sin(3A)+D22R5 sin(5A)
+D23R6 cos(6A)+D24(6R6xe2x88x925R4)cos(4A)
+D25(15R6xe2x88x9220R4+6R2)cos(2A)
+D26(20R6xe2x88x9230R4+12R2xe2x88x921)
+D27(15R6xe2x88x9220R4+6R2)sin(2A)
+D28(6R6xe2x88x925R4)sin(4A)+D29R6 sin(6A)xe2x80x83xe2x80x83(b)
where Dm (m is an integer of 2 or higher) are coefficients.
It should be noted that to design an optical system symmetric with respect to the X-axis direction, D4, D5, D6, D10, D11, D12, D13, D14, D20, D21, D22 should be used.
The above defining equations are shown to exemplify surfaces with a rotationally asymmetric curved surface configuration. Therefore, the same advantageous effects can be obtained for any other defining equation that expresses such a rotationally asymmetric curved surface configuration.
It should be noted that other examples of defining equations for free-form surfaces include the following defining equation (c):
Z=xcexa3xcexa3CnmXY
Assuming that k=7 (polynomial of degree 7), for example, a free-form surface is expressed by an expanded form of the above equation as follows:
Z=C2
+C3Y+C4|X|
+C5Y2+C6Y|X|+C7X2
+C8Y3+C9Y2|X|+C10 YX2+C11|X3|
+C12Y4+C13Y3|X |+C14Y2X2+C15Y|X3|+C16X4
+C17Y5+C18Y4|X |+C19Y3X2+C20Y2|X3|+C21YX4+C22|X5|
+C23Y6+C24Y5|X|+C25Y4X2+C26Y3|X3|+C27Y2X4+C28Y|X5|+C29X6
+C30Y7+C31Y6|X|+C32Y5X2+C33Y4|X3|+C34Y3X4+C35Y2|X5|+C36YX6+C37|X7|xe2x80x83xe2x80x83(c)
It should be noted that an anamorphic surface or a toric surface is also usable as a surface having a rotationally asymmetric curved surface configuration.
Further, the present invention uses an optical path distributing part whereby an image light beam emitted from the image display device at a divergent exit angle is led to the left and right ocular parts as stated above, and does not use an optical path splitting optical element such as a half-mirror. Therefore, a bright image can be observed.
It is desirable for the optical path distributing part to have at least two pairs of reflecting surfaces for the left and right optical paths of the viewing optical system for the left and right eyes that are arranged so that the axial principal ray entering the optical path distributing part in the left optical path is not in the same plane as the axial principal ray exiting the optical path distributing part in the left optical path, and the axial principal ray entering the optical path distributing part in the right optical path is not in the same plane as the axial principal ray exiting the optical path distributing part in the right optical path.
This is the minimum requirement to be met in order to form the left and right optical paths of the optical path distributing part so that these optical paths are not in plane symmetry with each other but in 180-degree rotational symmetry with respect to only a normal line passing through the center of the image display device.
Further, it is desirable for the optical path distributing part to have at least two pairs of reflecting surfaces for the left and right optical paths of the viewing optical system for the left and right eyes that are arranged so that the axial principal ray exiting the optical path distributing part in the left optical path is approximately parallel to the axial principal ray exiting the optical path distributing part in the right optical path.
This is a condition necessary to satisfy in order to place the decentered optical path plane of the left ocular part and the decentered optical path plane of the right ocular part in approximately parallel to each other.
Further, it is desirable for the optical path distributing part to have at least one pair of rotationally asymmetric curved reflecting surfaces having the function of correcting decentration aberrations.
Further, it is desirable for the optical path distributing part to have at least two pairs of rotationally asymmetric curved reflecting surfaces having the function of correcting decentration aberrations.
Further, the arrangement may be such that the optical path distributing part has at least three pairs of reflecting surfaces for the left and right optical paths, and the at least three pairs of reflecting surfaces are rotationally asymmetric curved reflecting surfaces having the function of correcting decentration aberrations.
It should be noted that each of the left and right ocular parts and the optical path distributing part, which constitute the viewing optical system, may be formed from only reflecting mirrors. Alternatively, each of the left and right ocular parts and the optical path distributing part may be formed from a decentered prism. It is also possible to integrate together the left and right ocular parts and the three-dimensional optical path distributing part into an integrated decentered prism.
When the left and right ocular part and the optical path distributing part are formed from a left ocular prism, a right ocular prism and an optical path distributing prism, respectively, it is desirable for the optical path distributing prism to include the following surfaces: an entrance surface facing at least the image display device so that both an image light beam for forming a left optical path for the left eye and an image light beam for forming a right optical path for the right eye enter the prism through the entrance surface; a left exit surface through which the light beam of the left optical path exits the prism; at least three left reflecting surfaces disposed in the optical path between the entrance surface and the left exit surface to reflect the light beam of the left optical path within the prism; a right exit surface through which the light beam of the right optical path exits the prism; and at least three right reflecting surfaces disposed in the optical path between the entrance surface and the right exit surface to reflect the light beam of the right optical path within the prism. The optical path distributing prism should desirably be arranged so that the entering optical axis of the axial principal ray incident on the reflecting surface closest to the entrance surface among the left reflecting surfaces in the left optical path is not in the same plane as the exiting optical axis of the axial principal ray exiting the reflecting surface remotest from the entrance surface among the left reflecting surfaces, and the entering optical axis of the axial principal ray incident on the reflecting surface closest to the entrance surface among the right reflecting surfaces in the right optical path is not in the same plane as the exiting optical axis of the axial principal ray exiting the reflecting surface remotest from the entrance surface among the right reflecting surfaces.
This arrangement is the minimum requirement to be met in order to form the left and right optical paths of the optical path distributing prism so that these optical paths are not in plane symmetry with each other but in 180-degree rotational symmetry with respect to only a normal line passing through the center of the image display device, as in the case of the above.
Further, the reflecting surface closest to the entrance surface in the left optical path and the reflecting surface closest to the entrance surface in the right optical path may be positioned adjacent to each other so as to face both the image display device and the entrance surface.
In this case, it is desirable that the optical path distributing prism should be provided with an anti-reflection member for an area including the boundary portion between the left and right reflecting surfaces closest to the entrance surface in the respective optical paths to prevent light rays emitted perpendicularly from the central region of the image display device from being reflected as ghost light.
Further, it is desirable that a distributed light reinforcing member should be disposed between the image display device and the optical path distributing part so that the light intensity of an image light beam emitted at a predetermined exit angle from each pixel located at least in the central portion of the single image display device is made higher by the distributed light reinforcing member than the intensity of a light beam emitted in a direction perpendicular to the surface of the pixel.
When the viewing optical system is formed from an optical path distributing prism and left and right ocular prisms, both the left and right ocular prisms may be arranged so that each ocular prism has, in order from the optical path distributing prism side, an entrance surface, a first reflecting surface, a second reflecting surface, and an exit surface, and the first reflecting surface and the exit surface are formed from the identical surface, and further the first reflecting surface is a reflecting surface using total reflection at the surface.
In this case, the entrance surface of each of the left and right ocular prisms may be formed from a rotationally asymmetric curved surface that corrects decentration aberrations, and the rotationally asymmetric curved surface may be a free-form surface having only one plane of symmetry.
Further, the second reflecting surface of each of the left and right ocular prisms may be formed from a rotationally asymmetric curved surface that corrects decentration aberrations, and the rotationally asymmetric curved surface may be a free-form surface having only one plane of symmetry.
Further, it is desirable to arrange the viewing optical system so that a relay image of the image displayed by the image display device is formed in the right optical path for the right eye and a relay image of the image displayed by the image display device is formed in the left optical path for the left eye.
Further, the image display device may be rotated through a desired angle about the normal line passing through the center of the image display device as an axis of rotation so that the horizontal direction of the image display area of the image display device is at an angle to a plane containing the exiting optical axes of the left and right axial principal rays exiting the optical path distributing part.
Further, it is desirable to satisfy the following condition:
20xc2x0 less than xcex8 less than 150xc2x0xe2x80x83xe2x80x83(1)
where xcex8 is the angle formed between the axial principal rays of left and right light beams led from each pixel located at least in the central portion of the image display device to the left and right eyes of the observer.
The condition (1) needs to be satisfied in order to separate the image light beams for the two eyes appropriately. If xcex8 is not larger than the lower limit, i.e. 20xc2x0, the effective diameter areas of the left and right optical surfaces, particularly those of the left and right first reflecting surfaces of the optical path distributing part that are closest to the image display device, undesirably overlap each other. Accordingly, the optical system has to be increased in size in order to ensure the required effective diameter areas and hence becomes unsuitable for use as the optical system of a head- or face-mounted image display apparatus. Conversely, if xcex8 is not smaller than the upper limit, i.e. 150xc2x0, an image display device having very wide viewing angle characteristics is needed. At the same time, the solid angle of the image light beam becomes small. As a result, it becomes impossible to observe a bright image. Regarding the angle xcex8, it is preferable to satisfy the following condition:
25xc2x0 less than xcex8 less than 120xc2x0xe2x80x83xe2x80x83(1-1)
The above-described image display apparatus can be used as an image pickup apparatus in which an image pickup device is provided in place of the image display device in the above-described arrangement. In this case, the pupil is arranged as an entrance pupil through which a light beam from a subject passes, and a subject image is formed on the image pickup device.
Further, the image display apparatus can be used as a projection apparatus in which a projection object is provided in place of the image display device in the foregoing arrangement. A screen is placed in front of the pupil to form a projected image of the projection object on the screen.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.